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My wife has a thing about tyre pressures. She has a habit of looking at the cars in our drive (the kids have cars too) and saying "that tyre looks a bit flat" and to save me saying that modern low profiles always look a bit flat I always check with my (cheapo) digital pressure gauge. (Actually, I don't, I usually say it looks OK to me). Anyway, today she filled up at Sainsbury's and said would I check her nice new (expensive) front tyres so I did. Programmed in the 2.4 bar at the front, 2.2 at the back, waited for the machine to ping etc. Then we drove home, - "does it feel as if the tyres are a bit hard?" says I on the way home. "yes " says she - so I checked them at home with my cheapo meter. Not 2.4 or 2.2 says the meter. More like 3.3 and 3.1. (Isn't that about 45 lbs per square inch I think, when it should be low 30s). So I checked my car's, which should be 2.3, and my (cheapo) meter said 2.3. Went to local garage with my car and their gauge said mine were 2.3. Conclusion? Sainsburys overinflated her tyres to the tune of about 15 psi. Unless of course my (cheapo) gauge and the local garage are underinflating them by about 15 psi ---- but how do I know?
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You might find your local IAM group have a contact who can check the gauge and give you an indication of how accurate it is.
A proper calibration would cost more than buying a really good gauge.
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Cheapo gauges can be good.
15 years ago I bought a made-in-Taiwan 12V air compressor complete with flashing light, lilo adapters and a dial gauge that read up to 220 psi [1]. A chap at work kindly gave the gauge a full-blown engineering certificated calibration [2]. It surprised both of us by being 100% accurate between 20 and 60 psi at various ambient temperatures.
A few years later I was given a couple of cheap pencil-type gauges which corresponded extremely well with the compressor gauge, which was good enough for me.
Recently, I read the Auto Express tyre pressure gauge review, which slated pencil-type gauges, and I shelled out £10 for the Accutire digital gauge that came out top.
Guess what? All 4 gauges still give the same reading on any particular tyre. This does not mean they are 100% accurate but it indicates to me that they are accurate enough.
PhilW, I would bet a virtual pint of Old Peculiar that the Sainsbury's tyre inflator is way out.
[1] It was marked down from £42 to £15 and as I was setting off to drive to Africa on my first expedition I thought it might come in handy. I rebuilt the compressor last year as the cylinder head nuts had come loose.
[2] well, I was also going to be doing some tyre testing.
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I bought an Accutire gauge as well. It's always been very accurate and has even shown the local supermarket forecourt (free) inflator to be fairly accurate as well!
Blue
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Phil,
As FiF advises - get a gauge and your local Weights and Measures office will check it for you free of charge.
Mine cost about £18-00 from Halfords and was within 0.01% at various levels up to 100psi.
Mine plugs in to the lighter socket and you pre-dial the prssure required.
Matt35.
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Visit:
www.chris-longhurst.com/carbibles/tyre_bible.html
And find the "Lies, damn lies, and tyre pressure gauges" section. Following HJ's advice, I have one of the ones illustrated on the left-hand side, purchased for less than £15 from what I think is called the American Tool Company.
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I think the source of my gauge was in fact:
www.international-tool.com
although it doesn't seem to be in their catalogue now, although other devices are.
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Nah, nah, nah, silly me: it's there top left, disguised as part of a gift pack including a multi-tool.
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Roger, I wrote to Chris Longhurst yesterday to ask him if he was aware of the Accutire range of digital gauges. I'll post again when I get a reply.
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Chris Longhurst wrote back saying that he did not see the Auto Express article in which the Accutire digital gauges did so well.
Try as I might, I cannot find a copy of the original AE test on the net. There are plenty of references to it but the original test report is so far elusive.
Does anyone have a copy of this or know where to find it? Blue Oval?
My Google search did show that Accutire digital gauges also finished top in a US ConsumerReports.org test in 2002. This assessment incorporated a ruggedness test which highlighted the vunerability of dial-type gauges to accidental knocks.
A copy of test can be found here:
www.retread.org/Inflation/index.cfm/ID/179.htm
and ABC action news reported it here:
abclocal.go.com/kfsn/features/consumerwatch/consum...l
"three digital gauges had performed flawlessly."
It seems that digital gauges have come a long way in the last five years and now rule the tyre gauge roost.
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Checked the AE site and the report is no longer there, my best guess is that it is due to be repeated soon, as they tend to cycle their product tests as far as I can tell.
However, it definately had an accuracy of 100% against their calibrated test equipment IIRC.
Blue
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The Halfords pump I bought, where you dial in the pressure, it hopelessly inaccurate e.g. set at (about) 32psi, you get 35. Set at (about) 35psi, you get over 40. I still use it but never rely on it, I always check it with a Cosmic dial-guage which came out tops on the AE test IIRC - and as use by the plod!
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Some years ago I was at a service station and was asked by an RAC patrol man if i had a gauge, and if so, would i like it checked.
Maybe all RAC / AA patrols have their gauges regularly calibrated.
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I'm sure a lot of this sort of thing goes on - especially IF somebody has just shoved in 50-odd litres of petrol, and the car feels 'different' anyway, would they bother to think the tyres had become under/overinflated?
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Thanks for the tips all. I also note that you have all been very polite and not asked how on earth anyone could put in an extra 15psi and not suspect something until driving away. My only excuses are :-
1. The gauge had flickering numbers due to the fact that I wanted "bars" but it went back and forth to PSI
2. The sun was shining on the digital readout which wasn't on the hose, it was on the machine & difficult to see
3. the last time I checked the tyres was about a month ago in the middle of that heat wave in France and I thought that they might now be underinflated in the cooler temps at the moment. (What by 15psi???!!)
4. Old age and sheer incompetence. My wife has just contributed that "excuse" and I have to say that she has probably hit the nail on the head. (Under my breath my reply was "You can check your own tyres next time" - but I didn't mean it, honest!)
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Phil, I've seen people partially deflate their tyres midway through a 500 mile hi-speed journey - I kid you not!
Reason: "But I always have them check my tyre pressures, oils and water when I put in petrol..."
So lowly-paid and ill-educated petrol jockey does what he's told, while ignorant owner sits on fat bum in car ...
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IMO, the only proper way to check your tyres is in your driveway, before you go.
The pressure can indicate considerably higher due to heat/expansion after even a fairly short trip to the garage and the quoted 'correct' pressures are for cold.
It's also worth checking 'reliable' tyres when there is a significant change in the ambient temperature from when you last did it.
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I had (before it fell to pieces) a Halfords digital inflator and also a pencil gauge and they both read the same.
I do not think that health and safety would allow Halfords to sell a machine that was inaccurate to a dangerous degree.
also, does it really matter if your tyres are actually 2.4 when it says they should be 2.3? I always think that it is more important that the opposite tyres are the same pressure.
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Tyres are just the most fantastic bit of kit on cars. They're amazingly abused - neglected, under/over-inflated, whacked by kerbs, etc - yet despite that they just keep on doing their job - certainly for most car drivers most of the time.
Me, I check pressures at least once a week - more if the temperature changes significantly or I do a 'car well loaded' journey - using various pencil type gauges (each new one has read the same as the old one I fear might be getting inaccurate). And I change tyres when I reckon they are starting to be unable to shift water too well; none of this 'legal limit' tosh.
Fussy? Maybe, but I demand performance from my tyres and, most importantly, my own and my passengers' safety depends on them. To do much less is bonkers.
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Agree with you completely, tyres are what keeps us on the road.
Myself, I check pressures every time I "fill 'er up", which is about every two weeks.
BTW, has anyone attempted to "play" with the pressure front or back only? I've heard, tested and confirmed that dropping a little the pressure on the back tyres makes the car oversteer just a bit more. Would be interesting to read others' experiences.
Vagelis.
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Yes, to an extent, if you drop the pressure on the tyres, you loose cornering grip owing to sidewall flex. You gain traction in a straight line (more rubber in contact with the road) and in mud or snow you might increase the ability to clear the tread. Trials cars always run quite low pressures.
If you raise the pressure you increase cornering grip owing to less flex in the sidewall. You loose traction in a straight line (less rubber in contact with the road) both accelerating and braking.
All of this assumes the variation is not excessive as other things will happen.
If you raise them too much you wear the middle of the tread, lower them too much you wear the outer edges. If all you do are motorway miles you will notice this very quickly.
Personally I do not run the book pressures on my Morgan, either road or track, but have raised them slightly on the road and raise them rather more on the track, but depending on the ambient temperature. But I avoid motorways, and since the car is mostly used competitively on the track, go round corners on the absolute limit.
I?m not quoting relative pressures as so much is a variable, but if you cannot feel the effect of 10% variation ? for heavens sake return it to normal!
Also I have heard of prosecution in France for this, but I suspect it was rather a gross and daft alteration which inspired it.
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Funnily enough, I just read a Which report that says the most consistently accurate gauges are the pen type ones.
The same report also said that tyre pressures given by manufacturers are only good for the original tyres and should be adjusted if you fit different tyres.
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Is there any way of finding out what the tyre pressures should be when alternative tyres are fitted to a car?
My Focus would normally be fitted with Pirelli P6000, but before I bought it the dealer fitted cheaper Kumho Ecsta tyres as the existing ones were very worn (yes I did see them first and they were evenly worn but with only about 3mm tread left).
The Kumho tyres specify a maximum pressure which is lower than the car handbook recommended pressure for full load for the rear tyres (by about 5 psi).
When I last checked the Kumho website, they did not have any information about the tyres (under construction).
I intend to replace them with Pirelli P6000s when the Kumhos wear out, but they're not wearing out fast enough!
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